1. Field of the Invention
The present invention relates, in general, to a backing plate for a brake shoe for use in a railway braking system and, more particularly, to a backing plate having end portions which stabilize portions of brake shoes which extend beyond the ends of a brake head.
2. Description of Related Art
Railway vehicles traditionally use a braking system wherein a brake shoe is forced against the wheel surface of the vehicle to provide a retarding force. The brake shoe is mounted to a brake head that is used to locate the brake shoe and provide the braking force to the brake shoe. The brake shoe has been constricted from a variety of materials, such as metal, wood, and more recently, composition friction material. Composition brake shoes for use in railway braking systems typically include a composition of friction material bonded to a steel backing plate. FIG. 1 shows an example of a composite brake shoe 10 mounted to a railway vehicle freight car brake head 13. This brake shoe 10 is bonded to a steel backing plate 15 such as with a binder material 14 and the assembly is held in place on the vehicle brake head with a key member 16. U.S. Pat. No. 4,466,513 to Dedek shows another example of a composition brake shoe for use in a railway vehicle braking system. U.S. Pat. No. 6,581,732 to Shute et al. shows a composition brake shoe having a backing plate wherein the brake shoe is attached to the brake head without the use of a key. The backing plate includes members disposed adjacent each end of the backing plate for securing the backing plate to a brake head.
Brake heads, such as those described above, and used on freight cars, passenger cars, transit vehicles and locomotives, are typically about 12 inches long. Brake shoes for freight cars and some passenger cars and transit vehicles are also 12 inches long. Some locomotives and passenger cars use brake shoes that are 14 inches or longer. These longer shoes increase the wear life of the shoe by increasing the volume of friction material and also improve the stability of the brake shoe and head as the brakes are applied.
FIG. 2 shows an example of an extended length brake shoe 18 mounted on a typically sized length brake head 20. The composite brake shoe 18 is bonded to a steel backing plate 21. The brake shoe 18, which is formed from a composition friction material, is secured to the backing plate via any known composition binder material 19 which has excellent impact resistance and high strength bonding characteristics. While the application of the binder composition material 19 in conjunction with the friction composition material is preferred, the composition friction material itself may have sufficient bonding characteristics as to be suitable for securing the brake shoe 18 to the backing plate 21. The brake shoe 18 has a predetermined length such that the end portions thereof 22 extend a predetermined distance beyond the ends of a brake head 20. These longer brake shoes 18 increase the wear life of the shoe by increasing the volume of friction material available for braking. The use of these longer brake shoes 18 also improve the stability of the brake shoe 18 and brake head 20 as the brakes are applied due to the increased surface area of the brake shoes 18. As shown in FIG. 3, under certain conditions, the end(s) 22 of the brake shoe 18 can experience sufficient force during brake applications to cause the steel backing plate to bend at bend point 24 around the end of the brake head 20. When this occurs, the composition friction material cracks 26 at the bend point 24. This friction material may even fall off of the bent end of the backing plate 21. Currently, the only resistance to this bending force is the inherent strength of the steel backing plate 21 and the composition material itself. In some instances, this resistance is insufficient to prevent bending or cracking.
U.S. Pat. No. 4,000,792 to Guldin discloses a brake shoe and head assembly that has been converted from wood brake shoe use to composition brake shoe use. As shown in FIG. 4 of the Guldin patent, each end of the composition brake shoe includes a tab extending from a partial backing plate portion of the shoe. Each tab includes a hole for receiving a screw therethrough. Each end of the brake head includes an anchor member that is aligned with the respective hole of each tab. The screw is then used to secure the brake shoe to the brake head. The tabs are used for attachment purposes as opposed to providing stabilization to the ends of the brake shoe. In fact, Guldin even teaches that the backing plate is segmented with gaps causing stress points between the tab portion and the central portion of the backing plate. Thus, the Guldin patent does not disclose the necessary structural design that would increase the strength of the brake shoe along the entire length thereof.
There is a need in the art for a single piece backing plate capable of providing sufficient strength and continuity along its length and having additional strength at its ends for supporting an extended length composition brake shoe. This additional strength at the ends of the backing plate stabilize the brake shoe and prevent cracking of the portions of the brake shoe which extend beyond the length of the brake head.